Different people find "fun" in different things. Field Day is fun for the planning, deployment, and operation of ham stations in the field. Some community outreach, some teamwork, some emergency preparedness, and some good practice.

I agree that actually operating during field day is less fun than at any other time of the year, unless you're in "competitive mode" and are trying to win the most contacts in your class. During these three days, the conversations are very short and mostly all the same, so there's not much "rag chewing" going on.

Field Day can also be fun in the sense that you may get permission to do things that you ordinarily could not do, such as operate a station in a public park, and camp there with it for two nights. Another "fun" element is improvising with what you have, such as setting up a station on the top floor of a parking structure in a metropolitan area.